Automatic bias control of an image display device in a video monitor

Abstract

A data display video monitor includes an automatic kinescope bias (AKB) control system for the type wherein kinescope cathode output pulses representative of the black current level conducted by the kinescope are produced in response to energizing the kinescope grid during sensing intervals. As a result of this operation, plural horizontal lines along the top edge of the visible display screen area are illuminated. To reduce the visible effect of the illuminated lines, the AKB system is activated for short sensing intervals (e.g., two seconds or less) between considerably longer holding intervals (e.g., five minutes).

What is claimed is: 
     
       1. A data display video monitor system comprising: an image display device for displaying data on a display screen thereof in response to a video data signal, said display screen including a visible area along an edge of said display screen which is normally devoid of displayed data;   means for exciting said display device during an excitation interval within a sensing interval to produce, at an electrode thereof, a signal having a magnitude representative of the condition of an operating parameter of said display device, said excitation of said disp1ay device causing a visible artifact to appear in said visible area along an edge of said display screen; and   control means responsive to said magnitude of said representative signal for providing an output control signal to said display device to maintain a desired condition of said operating parameter; wherein   each sensing interval is preceded by and followed by a holding interval;   each sensing interval encompasses a first plurality of vertical field intervals during which said visible artifacts appear; and   each holding interval encompasses a second plurality of vertical field intervals substantially greater than said first plurality of vertical field intervals, said visible artifacts being absent during said holding interval.   
     
     
       2. A system according to claim 1, wherein said excitation interval encompasses plural horizontal line intervals.   
     
     
       3. A system according to claim 1, wherein said display device is a kinescope with a grid electrode excited by said exciting means and a cathode electrode at which said representative signal appears.   
     
     
       4. A system according to claim 3, wherein said representative signal exhibits a magnitude representative of the black current bias condition of said display device.   
     
     
       5. A system according to claim 1, wherein said control means comprises: a charge storage device;   means for developing, at an output terminal, a signal having a magnitude related to the magnitude of said representative signal;   means for conveying said related signal to said charge storage device for developing said control signal across said charge storage device, comprising   (a) an amplifier having an inverting signal input, a noninverting signal input, and an output coupled to said inverting input;   (b) switch means having an input coupled to said output terminal of said developing means, a first output coupled to said charge storage device and to said noninverting input, and a second output coupled to said inverting input and to said output of said amplifier; wherein   (c) said switch means occupies a first position during said sensing interval for connecting said output terminal of said developing means to said first output of said switch means; and   (d) said switch means occupies a second position during said holding interval for connecting said output of said developing means to said second output of said switch means.